"The word that is being repeated often is insecurity, but the real word is war," he said.

"Let's recognise it. The world is in a state of war in bits and pieces," he said, adding that the attacks could be seen as another world war, specifically mentioning World War I and II.

"Now there is this one (war). It is perhaps not organic, but it is organised and it is war.

"We should not be afraid to speak this truth. The world is at war because it has lost peace."

About 15 minutes later, after an adviser spoke to him, Pope Francis took the microphone again as he was leaving the journalists' section in the plane and said he wanted "to clarify" that he was not referring to a war of religion.

"Not a war of religion. There is a war of interests. There is a war for money. There is a war for natural resources. There is a war for domination of peoples. This is the war," he said.

Upon his arrival in Poland to celebrate World Youth Day, Pope Francis also took on Poland's conservative Government, implicitly criticising its anti-immigration stance.

In a speech to President Andrzej Duda and his Government in Krakow's historic Wawel Castle, he pointedly called for "a spirit of readiness to welcome those fleeing from wars and hunger, and solidarity with those deprived of their fundamental rights".

"This means doing everything possible to alleviate the suffering while tirelessly working with wisdom and constancy for justice and peace, bearing witness in practice to human and Christian values," he said.

The Pontiff's five-day trip to Krakow is taking place in the shadow of a predecessor, John Paul, who has cult-like status in Poland for his role in inspiring his native country to stand up to communist rule in the 1980s.